Some conventional machines have a hydraulic power source for operating hydraulic actuators. For example, such a machine might typically include an internal combustion engine for driving one or more hydraulic pumps, which, in turn, supply power to one or more hydraulic actuators for performing work. One example of such a machine is a hydraulic excavator. A hydraulic excavator may typically include one or more hydraulic pumps, which provide hydraulic power in the form of pressurized fluid flow to one or more hydraulic motors and actuators such as a boom and a digging implement. In such a machine, the hydraulic motors may be used to rotate a cab relative to a chassis on which the cab is mounted and drive grounding engaging wheels or tracks for movement of the machine. Hydraulic power provided to the hydraulic actuators may be used to raise and lower the boom and manipulate the digging implement in order to perform digging and/or loading operations.
To increase the efficiency and/or reduce undesirable emissions resulting from operation of the internal combustion engine, efforts have been made to recapture some of the energy typically lost during operation of such a machine. For example, some energy is able to be recaptured in the form of stored hydraulic energy, and some energy is able to be recaptured in the form of stored electric energy via electric motor/generators. Thus, it may be desirable to perform some working functions in a machine with both stored hydraulic energy and stored electric energy by use of both hydraulic and electric actuators. However, in such a machine, the hydraulic actuators and electric actuators may have differing operational characteristics, which may result in undesirable operation (e.g., unbalanced responsiveness and/or speed).
Therefore, it may be desirable to provide a system and method for operating hydraulic and electric actuators in a manner that results in balanced operation, for example, when the requested operation of hydraulic actuators exceeds the maximum available hydraulic power of the machine. For example, such a system and method may control operation of hydraulic and electric actuators so that the hydraulic actuators and electric actuators operate simultaneously with anticipated responsiveness and/or speed, even when the requested operation of hydraulic actuators exceeds the maximum available hydraulic power of the machine. In addition, it may be desirable to provide a machine operator and/or service technician with a system and method for adjusting the balance of operation of hydraulic and electric actuators so that the balance between operation of hydraulic and electric actuators may be tailored to operate according to preferences of a machine operator.
A system and method for operating a machine having an electric motor and hydraulic actuators in disclosed in U.S. Patent Application Publication No. US 2008/0082240 A1 to Kagoshima et al. (“the '240 application”). In particular, the '240 application discloses a rotation control device for controlling the speed of rotation of an electric motor based on a hydraulic boom raising operation when simultaneously performing a rotation action and a boom raising action. According to the '240 application, acceleration of the electric motor is reduced based on the boom raising operation.
Although the system and method disclosed in the '240 application reduce the amount of acceleration of the electric motor based on the boom raising operation, the machine disclosed in the '240 application may still suffer undesirable operational traits. For example, the system and method disclosed in the '240 application does not account for situations in which operation of the actuators of the machine is limited to a predetermined maximum available power level (e.g., by machine design) or by capacity limitations of the power systems. In particular, operation of the hydraulic power sources and/or the electric power sources may be limited either by design, for example, in order to reduce strain on the various parts of the machine, or by virtue of a limit of capacity of the power of the machine, for example, when combined requests for operation of the hydraulic and/or electric actuators exceeds the capacity of the power sources of the machine. Therefore, it may be desirable to provide a system and method for controlling power in a machine having hydraulic and electric power sources that results in balanced operation of hydraulic and electric actuators, and further, to provide a machine operator and/or service technician with a system and method for adjusting the balance of operation of hydraulic and electric actuators so that the balance between operation of hydraulic and electric actuators may be tailored according to preferences of a machine operator.